Wireless Local Area Networks (WLANs) support uplink and downlink transmission between multiple stations (STAs) and access points (APs). One modulation format used in WLANs is orthogonal frequency division modulation (OFDM). In some WLAN systems, some of the STAs and some of the APs each have multiple antennas. When STAs and APs have multiple antennas (allowing for multiple input—multiple output, or MIMO communication), multiple streams can be transmitted in a given direction at the same time in the same wireless frequency bandwidth. Because multiple users can be served in this way, one name for such a multiple access scheme is MU-MIMO. A second multiple access scheme is orthogonal frequency division multiple access (OFDMA). Problems arise in MU-MIMO and OFDMA when channel conditions are unknown at the entity receiving the MU-MIMO or OFDMA signals.